Method for detecting acid anhydride-forming gases such as carbon monoxide and gaseous acid anhydrides



All@ l, 1950 w. E. BRINKER ErAL 2,517,382

METHOD FOR DETECTING ACID ANHYDRIDE-FORMING GASES sucH AS CARBON MNOXIDE, AND GASEOUS ACID ANHYDRIDES Filed Jan. 1o, 1945 I2v Sheets-Sheet l A gimen/ars 2,517,382 CID ANHYDRIDE-FORMING GASES SUCH AND GASEOUS ACID '\ANHYDRIDES Y 2 Sheets-Sheet 2 R BA am www m 1 mm 9 m. l o

n 1 uw uw d `n.. m A F Patented Aug. 1, 1.950 l 1PA Damn-romaine GASES lsperi .is enanos MoNoXnon AND `dAsnoUs doin ANHY.-

DRIDES William nnrinker and virgiro-fwi11iams,

Evanstonllll.,l

Application January 10, 1945, Serial` No. 572,212"

6 Claims. (Cl. Zit- 232) Our invention relates generally to an improved method and apparatus for the detection ofv gaseous acid anhydrides such as carbon dioxide and sulphur dioxide, particularly `:for the detection of small quantities of such gases and precursors thereof. such asfcarbon monoxide, inthe atmosphere.

In many instances, particularly in the opera tion of aircraft, there is an ever present danger that carbon monoxide from the aircraft engines, auxiliary engines, or heating systems, may leak, into the cabin. The fact that carbon monoxide is colorless and odorless'l renders it impossible for the crew to detectits presence, withnthe result that the members of the `crew lose consciousness without having become aware of the fact that toxic percentages of carbon monoxide were present in the cabinf It is therefore of `greatest importance `that the crew of an airplane havelso'me means for detecting the presence `oi toxiclfquan'tities of CO in the cabin air. Many attempts have been `made to provide such indicator, but in general have not proved entirely satisfactory because `of the `ex acting requirements `encotuitered in the use of such indicator upon an airplane. Inthe iirst place. the detecting apparatus must be verysen` sitive so as to detect minute percentages of 1GO in the` air. Secondly, the apparatus mustloper ate quicklyso as to provide an indication or alarm of the presencelof toxic percentages of CO- before the crew is seriously lale'cted. Thirdly, the lap-i paratus must withstand vibration, 'should not' be affected materially by large `variations in pressure and temperaturashould be :light in weight, portable, and rugged, and should be self-regenerative. 35 material, which is capable of dispersing the `air` It is thus an object of our invention `to proinminute bubbles. Withineach oi the compartvide an improved method and apparatus for inmentsmthereis an electrode, Apreferably made `of dicating the presence `of very small quantities of platinum. When the hydrogen ion concentration carbon 1nonoxide,acid anhydrides, and gases ca-` in one compartment of the cell exceeds that in pable of `forming acid anhydrides. the other, a difference in potential will exist be- .A further object `is to provide an` improvediap tween the two electrodes'. This potential difierparatus capable of giving an alarm when the ence may be ampliiiedby means of a vacuum tube percentage of CO in the air approaches values at voltage amplifier, preferably incorporating a which toxic effects may be expected. 45 bridge circuit, the output of the amplifier being A `further object is to .provide an improved suppiie'dto a suitable `electrical meter which may simple portable cellfor the detection oi the pres` be cahbrated to' indicate the percentage of CO ence of CO in air, utilizing a method based on present in the air being analyzed. thedetermination `of the hydrogen ion concen- The You-tiiiut` of the amplifier may also beuti tra-tion of water, or 'other suitableliquid, in which 50 lized to operate a relay when the output voltage theair and CO2. formedl by'the combustion ol or current exceeds a predeterminedwvalue, the CO, is .partially dissolved. l relay controlling the operation of any desired type `@ther objects will appear from the following of visible or audible signalpor the operation of` description, reference being had to the accom- Ventilating or Similar control means. pahying drawings, in. which: l l l 55 The apparatusutilized tocarry out the method lit?.

Fig. lis a owfdia'gram; l l

Fig. V2-is a longitudinal sectional view of -tl'iei cell, taken `on the 1ine-22Y of Fig. 3, with the cover in place; l l

Fig. 3 is a plan viewoi the cell, with the cover removed, portions of `the cell being shown in fragmentary section; l i

Fig. e is atransverse` sectional View tak-en on the line f4-4 of Fig.` 2; and l Fig. 5* is aftransverse sectional view, taken on the line tim-Eroi Fig; 2, and drawn to an enlarged scale. l l l In general, `the method of our lli-nvention is car ricdoult as follows: l

Air `to -be tested isdrawn `through a water bua` combustion ot any CO `which `may be present.A i. Two `flowing samples are iorced` `into separateV compartments of. a-icellcontaining water, or asalt.

solution, such as a potassium chloride orasodiu-m chloride solution, the compartments being Separated by `a pervious lwallsuch as glass wool or` i s, similar `porous..ortperforated medium,` `and are both` `connected `to `a, ,reservoir compartment .by small ports. Thexar owinginto these two `compartments of theme11 is admitted to the `compartmentsatthe bottom `thereof through dispersers f made of Acarbon, porous glass, or similar inert This `contini-lonely pumped is diagrammatically illustrated in Fig. 1, and com-- prises an air inlet tube I which is connected to the space from which the air to be analyzed is drawn. The tube I0 projects through the stopper I4 to the bottom of a flask I2, the ask l2 containing water. In bubbling through this water, the air sample has removed from it any foreign particles and gases which are readily soluble in water, and the air is substantially saturated with water vapor. The air is withdrawn from the top of the flask I2 by a motor driven pump I6 and forced through a soda lime filter I8. This filter is effective to remove all of the usual constituents of the air except CO, oxygen, nitrogen, hydrogen, and the rare inert gases, argon, neon, xenon, and krypton. The scrubbed air from the lter I8 flows through a tube 2U which is divided into tubes 2| and 22 to provide similar parallel paths.

Within an enlargement of the tube 2| there is located a platinum wire 24 connected by sealed lead wires 25 to a source of electrical energy, illustrated as a battery 2li. The voltage supplied to the platinum wire 24 is sufficient to maintain it at a temperature of incandescence. As a result, any CO in the air flowing through the tube 2|, will be ignited, combining with the oxygen in the air to form carbon dioxide. Since the CO2 in the original sample was removed from the air by the soda lime filter I8, the air flowing from the pipe 2| will contain a percentage of CO2 drectly proportional to the percentage of CO contained in the original sample. The tube 2| is connected to a disperser 28, While the tube 22 is connected to a similar disperser 29. The dispersers 28 and 29-l are located near the bottom of compartments 3U and 3|, respectively, of a cell 32.

Within the compartments 33 and 3| are suspended platinum electrodes 34 and 35, respectively. Platinum has been found to be one satisfactory metal for the electrodes, but reasonably satisfactory results may be obtained by the use of other conducting electrodes which are inert with respect to the liquids in which they are immersed, such, for example, as gold, carbon, antimony, tantalum, aluminum oxide, palladium, as well as other substances. The compartments 3U and 3I are separated by a porous Lpartition 38, while the two compartments are connected by small ports with a reservoir chamber 4|). The electrodes 34 and 35 are connected to the input terminals of an amplifier 42, the output of which is connected to a suitable electric meter 44 which is representative of any suitable indicating or relay device to be actuated by the output of the amplifier 42.

The .particular construction of the cell 32 which has been found to be satisfactory, is more clearly shown in Figs. 2 to 5, inclusive, as comprising an oblong metal shell U having a flange 52 at its rim. The shell 50 is preferably lined throughout with a coating 54 of a synthetic rubber, such as Buna-N. The rubber lining is also conformed to provide a partition 56 provided with four ports 58. These ports connect the tdp and bottom of compartments 36 and 3|, respectively, with the reservoir chamber 40. A metal cover 6|] having a synthetic rubber lining 62, is bolted to the flange 52.

As best shown in Fig. 5, the electrodes 34 and 35 comprise sheets of platinum foil 64 supported by rectangular platinum wire frames 66. The electrodes have conducting wires 68 welded thereto, These wires, as well as support wires B9, ex-

tend through insulating grommets 'I0 mounted in the cover 60, 62.

As best shown in Figs. 3 and 5, the wall 38 between the compartments 30 and 3|, is composed of a pair of perforated plates 14 and a hollow rectangular frame 16. The plates 'I4 and frame 'I6 may be made of a suitable plastic, such as polystyrene. The space enclosed by the frame 'I6 and between the perforated plates I4 is packed with fine glass wool 18. The partition 38 is held in place by fitting into suitable grooves formed in the synthetic rubber lining 54, as well as in the cross wall 56.

AS best shown in Fig. 2, the difusers or dispersers 28 and 29 are located respectively at the bottom of the compartments 3|) and 3|, and have the tubes 2| and 22 connected thereto respectively in any suitable manner, as by rubber tubing. The cell 4u is substantially filled with water, preferably containing a suitable salt. Dilute solutions of potassium chloride and sodium chloride have each been found satisfactory. AAir may escape from a vent port '19. This port may be closed by suitable air escape valve which will block the escape of liquid from the cell.

In using the apparatus, the pump I6 is operated and the platinum burner 24 and amplier 42 are electrically energized. As the` air is bubbled through the water in theV flask I2 and through the soda lime filter I8, most of the impurities are removed. CO being but slightly soluble in water, and not reacting with'sodalime, passes through the burner and forms CO2.

CO2 bubbling through the water in compartment 3U, decreases the pI-I Valueof the liquid in compartment 30. No comparable decrease occurs in the pl-I value of the liquid in compartment 3|.

Since the compartments 33 and3| are in electrical communication through the interstices in the glass wool partition 38, it is found, that a measurable difference in potential will be present upon the electrodes 34 and 35 when a very small percentage of CO2 is present in the air dispersed in the compartment `30. While this potential difference between the two electrodes is of the order of a fraction of a volt, it maybev amplified so as to provide an accurate reading upon the meter 44, which may be calibratedto indicate the percentage of CO in the air sample being analyzed. This potential difference may be due to the contact potential at the interface or junction of the liquids in the two compartments 30 and 3|. Y

The dispersion of the gases in the compartments 3D and 3| causes a certain amount of circulation of the liquid in these compartments, and

In normal use of the apparatus, the pumpis.

operated continuously, so that the meter 44 will at all times indicate the percentage of CO in the air being analyzed, and any alarm' device connected to the output of the amplifier 42 4will be energized if at any time the percentage ofk CO approaches a predetermined value, for example,

The

attirance a concentration fat which "theairbecomes toxic. 'Il he .apparatusis self-regenerating, in thatafter ahigh concentration of CO in the airanalyzed has been indicated bythemeter, if thedegree of concentrationb'f"COintlie 'airis decreased,"the meter will indicate this fact with buta Very short period of lag. i i t When the apparatus is to be `utilized forthe determination of theiconcentrationA of gases other than CO, fthe apparatus will be suitably' modified sofas to remove the acid anhydride from one `of the'two parallel flow paths leading respectively to`the'two'compartments of the cell, whileit .is permitted to remain in the gas supplied to the other compartment. This can usually be accomplished by utilizing an appropriate llter or scrubbe'r which will remove the gas for which the analysis is to be made from one-half of the sample, while the remainder of the sample is bypassed around such filter or scrubber. In this way the apparatus may be used for the detection or determination of the percentage concentration of any one of a plurality of different acid anhydrides By the method of analysis for CO described herein, it has been found that extremely minute percentages of CO in an atmosphere may be detected. A concentration in the order of ten parts of CO in a million parts of air may readily be measured. In fact, the method is such that the sensitivity increases with decreased concentration of the CO. This may be explained by the fact that the potential developed across the electrodes is determined by the logarithm' of the ratio of the activity of the solution in one of the compartments relative to the activity of the solution in the other compartment.

The electrochemical formula may, for the sake of simplicity, be reduced to the following equation:

a E=K log da in which E is the potential difference generated across the electrodes; K is a constant; a' is the activity of the solution in the compartment 30; and a0 is the activity of the solution in the compartment 3|. Since the temperature and pressure within these two compartments are equal, these factors, as well as others, need not be considered, or may be assumed to be included within the constant K. From this formula it will be apparent that as a increases in value, for example, from 0.001 (logarithm-3.00) to 0.010 (logarithm-2.00), the electrical potential diilerence across the electrodes will change by the factor 2/3. Because of this relationship it appears that under properly controlled conditions, the method of this invention may be employed to detect concentrations of CO in air of as low as one to ten parts in a billion. This is possible because the potentials developed are not proportional to the concentrations, but are proportional to the logarithm of the concentration, and therefore a relatively slight change in concentration causes a greatly magnified (mathematically and actually) change in the potential developed.

In addition to utilizing this method of CO detection and analysis in aircraft, it may be used for the detection of dangerous concentrations of CO in the atmosphere of garages, homes, various industrial plants where the presence of carbon monoxide, acid anhydrides, and precursors of acid anhydrides may be present in the atmosphere. With suitable variations in the apparatus, the

methodlmay:alsotbeemployediforlanalysisfortlue gases :andisimila-rfgaseous mixturestin" whlc CG, other `precursors of acid anhydrides, `:er :Taelman-L hydrides maybe expectedto the present iandltheir concentration esterniined.` l

While wehaveishown and fdescrib'ed arparticular method and `a particular apparatusifor forming the method, it willLbeunderstoodfbythose Skilled in the V"art Vtl'ia't the nithd` may'be'lvaiied, and 'variations "the apparatus 'may lbe made, without departing' from lthe underlying Lprinciples oitheiinvention. "We thereforedesirefbyfth fllowing `clainfis, to include Awitllinfthe rscope our inventionall such equivalent.lmethodsandvappairatus by whichIsubstaritialiytneiresultslot ourfim vention may `be obtained th'roughlthe perforin'l-i ance of substantiei-lly equivaleritptepsnor *incluse of "substantially lequivaliit apparatus. 'i

l. The method of determiningthe'presencenf a sm'all 4percentage rof""carbfon monoxide in a gaseous `mixture sample `eont'aiining oxygen, which comprises, removing from the sample substantially all acid anhydrides, dividing the sample into two substantially equal parts, converting the carbon monoxide in only one of the parts of the sample into carbon dioxide, utilizing the oxygen in the sample, dispersing the two parts of the sample respectively in two portions of an aqueous solution separated by a solution pervious medium, and measuring the electrical potential difference ltoetween the two portions of the aqueous soluion.

2. The method of determining the presence of a small percentage of carbon monoxide in an air mixture sample which comprises, removing from the sample substantially all acid anhydrides, dividing the sample into two substantially equal parts, converting the carbon monoxide in only one of the parts of the sample into carbon dloxide, dispersing the two parts of the sample respectively in two portions of an aqueous solution separated by a solution pervious wall, and measuring the diierence in hydrogen ion concentration in the two portions of the solution.

3. The method of determining the presence of a gaseous acid anhydride in a sample of air which comprises, removing the gaseous acid anhydrides from one-half of the sample and dispersing this half of the sample through an aqueous solution in one of two compartments separated by a pervious partition, dispersing the other 'half of the sample containing the gaseous acid anhydride through the aqueous solution in the other compartment, and measuring the difference in electrical potential of the solutions in the compartments.

4. The method of determining the percentage of an acid anhydride forming gas in a gaseous mixture sample which comprises, removing from the gaseous mixture all acid anhydrides, dividing the sample into two substantially equal parts, converting the acid anhydride forming gas in one of the parts of the sample into its acid anhydride, dispersing the two parts of the sample respectively in two portions of an aqueous solution separated by a pervious medium, each portion containing an inert metallic electrode, and measuring the electrical potential difference between the two electrodes.

5. The method of determining the percentage of an acid anhydride forming gas in a gaseous mixture sample which comprises, removing from the sample substantially all acid anhydrides, divlding the sample into two substantially equal parts, convertingtne acid anhydride forming gas in one of the'parts of the sample into its acid anhydride, dispersing the two parts of the sample respectively invtwo portions of an aqueous solution separated by a water pervious partition, and measuring,r the electrical potential difference between the two portions ofthe aqueous solution.

\ 6.,The method of detecting the presence of toxic percentages of carbon monoxide in air which comprises, continuously dispersing in an aqueous solution a sample of the air from which acid forming anhydrides have been removed, causing combination of carbon monoxide with ogygen in an equal portion of the sample to form carbon dioxide, dispersng the sample containing the lcarbon dioxide in an aqueous solution separatedfrom the rst mentioned aqueous solution by a porous partition, and measuring the electrical potential difference between the two aqueous solutions.

WILLIAM E. BRINKER.

V'IRGIL C. WILLIAMS.

REFERENCES CITED The following references are of record in th le of this patent:

UNITED STATES PATENTS Number Name Date 1,375,933 Rideal et al Apr. 26, 1921 1,560,660 Cain Nov. 10, 1925 1,893,490 Beekley Jan. 10, 1933 1,900,884 Lusby Mar. 7, 1933 1,944,803 Ornstein Jan. 23, 1934 2,373,111 Francis Apr. 10, 1948 2,400,923 Farr May 28, 1948 FOREIGN PATENTS Number Country Date Germany Dec. 11, 1918 

3. THE METHOD OF DETERMINING THE PRESENCE OF A GASEOUS ACID ANHYDRIDE IN A SAMPLE OF AIR WHICH COMPRISES, REMOVING THE GASEOUS ACID ANHYDRIDES FROM ONE-HALF OF THE SAMPLE AND DISPERSING THIS HALF OF THE SAMPLE THROUGH AN AQUEOUS SOLUTION IN ONE OF TWO COMPARTMENTS SEPARATED BY A PERVIOUS PARTITION, DISPERSING THE OTHER HALF OF THE SAMPLE CONTAINING THE GASEOUS ACID ANHYDRIDE THROUGH THE AQUEOUS SOLUTION IN THE OTHER COMPARTMENT, AND MEASURING THE DIFFERENCE IN ELECTRICAL POTENTIAL OF THE SOLUTIONS IN THE COMPARTMENTS. 